Method of controlling the condition of a medium



u 19, 1940- c. H. STEVENSON 2,193,845

unflion "0F QQNTROLLING TBE CONDITION OF A MEDIUM Filed Aug. 12, 1938 ilk 88 89 9 Patented Mar. 19, 1940 METHOD OF THE CONDITIO a mum Gary H. Stevenson, Chicago, Ill, assignor to Lindcoring Company, Chicago, 111., acorberg Ensin notation of Illinois Application smtiiaglgsg serial No. 224,457 7 scum (01. 230-) This application is a continuation in part of application Serial No. 97,444, filed August 22, 1936.

The method of the present invention is intended to afford an automatic control for a mediumsuch as the heat admitted into a heating furnace or for otherwise controlling the physical or chemical condition, or volume of a physical substance, or an attribute or quality thereof, but for pres.- ent purposes and in order to more clearly define the nature of the present invention, I shall explain the details of the present method as applied to a heat treating furnace in which it is desired to maintain the temperature at a substantially uniform degree despite variations in the depletion of the heat due to changes in the load conditions or in the gas pressure or other variable factors which attend the operation of an apparatus of this character.

The method of the present invention differs from others with which I am familiar, in that it makes provision for the accurate measurement of any excess or deficiency in temperature during a relatively short period, and recurrently resets the valve or other control member in ratio thereto through a series of diminishing fluctuations until substantially stable conditions are attained.

In measuring the excess of the temperature or other variableiactor with accuracy, I find it first of all necessary to make provision for the complete cutting off of the incoming supply "of gas or the like, and thereafter, through a time interval which is predetermined by the excess, to subject the valve to a readj 'tment of proper amount until an adjustment is obtained which maintains the temperature within the control range, which thus terminates the period of recurrent adjustments until further substantial fluctuations in temperature occur as a result of changing conditions which require a repetition of the adjusting operations.

In order to carry out the operations above enumerated it is necessary first of all to employ an element which is responsive to changes. in the conditions/ of the medium under control, and in the case of a furnace, a thermocouple, delicately responsive to changing conditions, will be employed, although it will be understood that where i a medium of difierent character is employed, a. suitable responsive element adapted to such 'con-' ditions will be substituted in place of the thermocouple.

In order to utilize a thermocouple or the like, it is necessary to establish a control range or a few degrees variation, having high and low limits and including the intended temperature as the medial condition; Such a control range is necessary to permit the responsive device at the high and low levels of the control range to set in at the respective degrees of temperature or the like represented by the high and low limits of the control range; v

When the high it is registered by the .thermocouple, mechanisms will be actuated which serve promptly to cut off any additional supply of gas during the period of measurement of the' excess heat and readjust the valve controls to reset the valve for a lesser admission of gas. similarly whenr the thermocouple attains the lower limit of the control range, mechanisms are actuated for admitting gas in greater amount, j I

until through a series of such fluctuations the stable conditions are attained.

It has been found from experience that accu- I rate regulation of the gas valve or similar con-V trolling device cannot be made so long as the, gas isbeing admitted during the period of readjustment, since the inflow ofgas during this interval introduces a disturbing factor which makes it impossible to accurately measure the excess heat previously admitted, so that the present invention is designedto effect the necessary measurement of excess during the interval while the valve is closed and while thethermocouple measures the amount of temperature in excess of the upper limit of'the control range and the mechanisms employed are properly timed to efiect the necessary readjustment of the valve control mechanism during this interval, without, however, opening the valve itself until the temperature falls into the control range, after which the valve is opened in a reduced amount determined by the previous setting of the valve control mechanism.- 1

In this way the necessary adjustments are effected in properly timed relation, so that after a few fluctuations, due to the presence of variable factors, an accurateadlustment is ultimately at- PATENT caries},v

tained which admits gas in an amount just sufficient to compensate for the heat depletion in the furnace and promptly effects a readJustment whenever the depletion rate is disturbed by in- 5 creasing or diminishing the load of materials introduced into the furnace for heat treatment,

or by other factors which determine the supp y of gas which must be admitted to maintain the intended temperature.

In order to more fully point out the nature of the present method as applied to a heat treating furnace, reference is had to the accompanying drawing, wherein,

Figure 1 is a diagrammatic view showing a heat treating furnace with the valve mechanisms and controls actuated through electrical circuits; and

Fig. 2 is a greatly magnified view of a graph produced upon a record strip traveling forward at uniform speed and representing the control range with an undulating line inscribed thereon by a stylus and representing changes in temperature as indicated by the movements of the thermo-couple.

It will, of course, be understood that the present mechanism is illustrative only, and that electrical circuits are employed merely as a matter of convenience for the transmission of the re quired movements, and that pneumatic circuits or mechanical connections might readily be employed in lieu of those shown in the drawing.

As illustrated, the method is applied to a heat treating furnace ll of the character employed for the heat treatment of metallic objectssuchr as springs, shafts, tubes or the like, which require a heat treatment through a Properly computed period and at a controlled temperature. In order to register variations in temperature, a thermocouple ll of any suitable character is 0 employed, which is connected through circuit wires'll-withg galvanometer I! or the like of a character well understood in the art, which actuates a swinging arm II in either of two directions, depending upon the rise or fall of the 45 temperature.

The swinging arm carries a contact C, which upona rise in temperature is positioned to engage the contact H, and upon the fall in temperature to engage the contact L. when the so temperature in the furnace is within the restricted control range of a few degrees, the swinging arm It will occupy the medial position shown and be out of engagement with the contacts H and L.

as Electricity is supplied from a power line which comprises the wires I and IS. The swinging arm II is connected with the wire I! through a lead II. The contact L is connected through a wire I! with a coil ID, of reversing motor II,

so which when energized serves to establish conditions permitting an increased opening of the valve 20, and the coil l9 acts in opposite direction to a companion coil 2i, which when energized. operates, through proper controls, to re- 66 duce the extent of the valve opening.

In Figure 1, the closing position of the valve is indicated in full lines, and a partiallyopened position is indicated in dotted lines. The valve controls the admission of'gas and air through 7 pipes 22 and 23 to a burner is connected with the furnace. In of the fact that the companion'colls I! and 2t act oppositely to respectively establish an increased or diminished valve opening,

1s these coils may be properly referred to respecarcane tively as the valve increasing and the valve reducing coils, and it is by properly timing the energizing of these respective coils in ratio to a measured deficiency or excess in heat, as the case may be, that it is possible to properly set the controls which govern the opening of the valve at the proper time and. in the proper amount to correct the error and establish and maintain the intended conditions.

The valve reducing coil 2| operates during the interval that the swinging contact C engages the contact H by reason of an excess of temperature in the furnace above the control range, and this coil is connected with the power line I through a lead 25 which also connects with the valve increasing coil IS. The coil 2| is also connected by a circuit wire 26 to the contact H, and to a wire 21 which leads to a coil 28 surrounding a pole piece 29 which carries an armature ll, the arrangement being such that when the swinging contact C engages the contact H upon an excessive rise of temperature, the coil 2! will be energized and the armature 30 lifted to open a circuit through contacts 3| and 32 and establish a circuit through contacts 33 and 24.

The contacts 3| and 33 are connected with a circuit wire 35 which connects with the line wire IS. The contacts 32 and 34 are connected with a valve actuating motor 36 through circuit wires 31 and 38, the former of which makes direct connection with the motor, and the latter of which is connected through a limit switch 3!, and which is operated through a time interval controlled by the coils l9 and 2|, so that the position of the limit switch will correct the conditions of previous deficiency or excess of heat in the furnace, as the case may be, in a manner presently to be described in detail.

The motor is a reversing motor and is connected with the line wire i6 through a return wire II which is common to either of the circuits established through the wires 31 and 20 for energizing the motor in the proper manner to operate the valve in the intended direction and to the extent permitted by the limit switches a and 4i. The limit switch 39 is carried by a worm gear ll which is freely mounted upon the shaft 42 of the motor 36, and the shaft has keyed thereon an arm 43 which is connected with the valve arm 44 through a link II, so that when the valve operating motor 36 is energized to operate in the proper direction, the arm 43 will be rapidly shifted through the range of movements permitted by the adjustable limit switch 39 which permits a variable opening of the valve, and a fixed limit switch 46 which breaks the motor circuit at the instant the valve has reached its closed position.

The limit switch 39 comprises spring contact fingers I and 48, the latter of which overhangs the former and is adapted to be lifted by the contact of a plunger 49 carried by the arm 0, sothat, assoonasthevalvehas been openedto a previously computed extent, the circuit will be broken and the motor will stop. A second plunger ll on the arm coacts with the limit switch ll in a similar way. The circuit wire ll leads to the finger I and cooperates with a return wire I leading to the motor, so that, when the motor is energized in a valve opening direction, the circuit will be established as follows: From line wire I! through wire as, contacts a and I2, armature 3., and contact wire 38, contactflnlcrs ll and ll, andwire ",throughthe greases motor, with-the return to line wire I! established through the wire 40.

The circuit for closing the valve is established as follows: From line wire I! through wire 35, contact 3.3, armature 30, contact 34, and wire 31, through the limit switch 46, to the motor, with the return through the wire 40 to the line wire l6.

The worm gear 4| which carries the limit switch 39 is rotated at apredetermined slow rate by either the-valve increasing coil It or the valve reducing coil- 2|, which; impart motion through a reversing motor ii andfriction clutch 52 to a threaded shaft which also. carries a worm 54 in mesh with the worm gear 4|. The threaded shaft carries a rider 55 having a pointer 56 which registers with the markings on a gage plate'51 inscribed to indicate the percentage of opening 'of the va1ve at any given position of the pointer.

' Operation In use, thereg ulating' movements of the above mechanism ar'e reflected upon the graph shown in Fig. 2, in which the sinuous record line A represents changes in temperature as measured by the thermocouple. The record line traverses and intersects a. control zone M having an upper limit represented by the dotted line D and a lower limit represented by the dotted line E.

The ideal condition toward which the regula 'tion tends is represented by the upper flattened I end of the graph line which lies wholly within lifts the pole piece 29 with its armature 30 and establishes a circuit through the wires 35, 31 and 40, which is the valve closing circuit and operates to quickly close the valve by the fall of the arm 43 to the position shownin full lines in Fig.

1.- This immediately shuts-off all further supply of gas to the furnace, and initiates the measuring period during which the excess temperature over and above the control zone is registered in a readjustment of the limit switch 39 by a clockwise movement to bring thecontact fingers 41 and 48 to a lower position than previously, so that on the next'ppening valve movement the valve will open to a lesser degree than previously.

The excess temperature entering the furnace 1 after the valve has been closed is represented on the graph by the first peak lying beyond the upper limit line D and between the points B and 1 F represents the point at which the excess heat has been exhausted and the temperature again falls to the upper limit of the control zone, at which point the swinging contact C will move away from engagement with the contact H 1 and thus terminate the limit switch adjusting operation effected .by the energizing of the valve reducing motor 2| during the interval of time represented on the graph line D between, the points B and F. Since the motor when energized operates at a uniform speed, the length of this line 3-! represents the period of time during which the limit switch is being adjusted in a clockwise direction and the extent of that adjustment. From the above it will be evident that the time consumed in the adjustment of the limit switch and hence the extent of itsadjustment is commensurate with the period of time required'to dissipate the excess of heat represented'by the peak between B and F.

The disengagement of the contacts 0 and H also deenergizes the coil 28, allowing thearmature 30 to drop and establishing circuits from the line Ii, through 35, 3|, 30, 32, 30, 41, 48, W and 40, to the line l6, thereby opening the valve to the extent permitted by the previously adjusted limit switch. Despite the instant opening of the valve, the temperature may continue to fall through. the left hand peak represented between G and J, but will ultimately begin to rise and continue rising untilthe record line traverses the control zone at the point B, at which point the valve will be promptly closed and the period of time required to dissipate the excess of temperature between the points 3' an'd'F' will result in the -moving of the limit switch again in the closing direction but to a lesser extent, as represented by the ratio between the lines B-F and B'--F'.

' Again the temperature may fall below the control zone and again rise above the control zone, with a' further and lesser adjustment of the limit switch, until by alternating stages a final adjustment of proper degree is reached which will eliminate the fluctuations and cause the temperature to remain within the control zone, as indicated by the final straight line of the graph beyond the final fluctuations represented at B It'will be seen from the foregoing that the fluctuations represented by the peaks above the control zone progressively diminish in extent, and that the corresponding adjustments ofthe limit switch become more and more delicate, until an exact ratio is established between the input of heat into the furnace and the depletion thereof so that after a short interval-of time the valve will be accurately adjusted to constantly supply the required amount of heat to compensate for the depletion thereof'.

If an over correction results, adjustments occur on the low side of the control zone. During the interval between G and J, the heating rate is advanced to counteract an over correction of the limit switch by a counter-clockwise movement of the required extent, and similarly in the following cases in which the record line falls below the lower limit line E.

Theoretically, it, might be possible, by the first measuring oil of the time required to dissipate I the excess. in the amount of heat, and by reducin thevadmissi'on of gas in" ratio thereto, to accurately adjust the valve. This might be possible if the speed of the correcting motor 5| were attuned exactly to the particular furnace, and no variables were present in gas pressure, operating temperatures, loading, and so forth,'sin'ce in the absence of suchvariable factors the time for the excess amount of temperature to be absorbed would correspond exactly to the computed jadjustment of the' valve. Due to practical conditions, however, it is seldom possible to exactly adjust the valve on the first correction, and diminishing fluctuations will thereafter occur until the correct adjustment. is attained as the resultant of the closing and opening movements of the valve occasioned as the temperature rises above or falls-below the control zone, although.

The ultimate adjustment will thus, inmost cases, be the resultant of alternate closing and opening movements of the limit switch during time intervals commensurate with the condition of the furnace during the period of regulation, although it will be understood that the adjustments effected on the high side of the control range will be mainly relied upon, because such adjustments are computed during an interval, or substantially so, while the gas supply is entirely turned off, since the closing of the valve will occur promptly as compared with the relatively long period of time during which the limit switch is being actuated.

On the low side of the control zone, however, the opening movement of the limit switch will immediately occasion a further opening of the valve which will follow the movements of the limit switch during the interval of time measured by the length of the record line G-J, which represents the period during which the limit switch is being retracted by a counterclockwise movement.

The width of the control zone represents the medial position within which the swinging contact C is out of engagement with either the contact H or L, so that, during this interval, neither of the adjusting motor coils I9 and 2| is energized, so that no adjustment of the limit switch will be effected during the interval of the temperature in the control zone.

The invention is one which so times the adjusting operation as to effect a more accurate measurement of the extent of readjustment required to dissipate an excess in the amount of heat occasioned by a previous adjustment than would be possible if the adjusting operation were performed during an interval of time while disturbing influences were present, or in conformity with any system which seeks to immediately readjust the valve to a new setting without first closing off the heat supply and thereafter timing the period required to dissipate the excess as a gage whereby to definitely determine the repositioning of the mechanism which controls the resetting of the valve.

As before stated, the mechanism here shown serves simply to illustrate the application of the present method to the control of temperature in a heat treating furnace, but in view of the fact that the method is applicable to numerous and diversified conditions, it is thought desirable to define certain of the terms employed in the appended claims.

It will therefore be understood that the term medium is intended to define any substance, material, or agency, which is subject to measurable fluctuation, either in quantity, or in its physical, chemical, or electrical attributes, by reason of variations in the inflow as compared with the depletion to which the medium is subjected. I

The term conditioning factor refers to the admitted substance or agency, whether physical, chemical or electrical, which serves to replenish the medium to compensate for depletions therefrom, whether the conditioning agency he in the nature of an additional supply of the same substance of which the medium is composed, or whether it be a physical, chemical or electrical attribute, which qualifies or modifies the state of the medium.

The term responsive has reference to an element or agency which is influenced in measurable degree by the conditions within the medium, and which is capable, through appropriate means, of controlling said conditions and of maintaining escapee a state of substantial stability or uniformity therein at the intended level.

The term control zone has reference to a limited but permissible range of fluctuations within the medium between upper and lower liniits which include the desired'level and having a sufficient range to enable the responsive element or agency to be selectively actuated when conditions within the medium attain the upper or lower limits of the control zone, as the case may be.

The term upper and lower as related to the control zone has reference to the presence of a greater or lesser quantity of the conditioning factor, whatever it may be, and does not necessarily refer to a greater or lesser degree of temperature, since the upper limit of the control zone might properly indicate the lowest permissible temperature as in the case of a refrigerant in which an excess of the refrigerant would be represented by a lower degree of temperature, while a deficiency in a refrigerant would be represented by a higher degree of temperature. It will thus be understood that in all cases the term upper and lower" has proper relationship to the character of the conditioning agent, although in the regulation of a furnace of the character particularly described the term upper and lower" would of necessity correspond to a greater or lesser degree of temperature, while in the case of a refrigerant the term upper and lower would bear inverse ratio to the temperature.

The term "valve is intended to refer to any appropriate element or agency adapted to regulate the admission of the conditioning factor in the amount required to maintain stable conditions within the medium.

The appended claims are intended to cover and define any system of the general character described, which conforms to the language of the above definitions.

I claim:

1. The method of maintaining a stable condition in a medium at a substantially even level within the limits of a restricted control zone, which consists in admitting a conditioning factor at a predetermined rate until the upper limit of the control zone is reached, promptly shutting off the supply of the conditioning factor at the upper limit and maintaining it shut off while the condition of the medium remains above said limit, measuring the excess amount of condition within the medium according to the time said condition remains above said upper limit and providing for the subsequent readmission of said conditione ing factor in a reduced amount dependent upon the measurement, again admitting the conditioning factor in such reduced amount as soon as the condition within the medium falls to the upper limit of the control zone by reason of the dissipation of the previous excess of the conditioning factor, increasing the rate of admission of the conditioning factor while the condition of the medium remains below the lower limit of the control zone, and continuing said operations by stages which cause the condition of the medium to progressively approach the desired level by diminishing fluctuations until a stable condition within the control zone is attained.

2. The method of maintaining a stable condition in a medium at a substantially even level within the limits of a restricted control zone, which consists in admitting a conditioning factor at a predetermined rate until the upper limit of the control zone is reached, promptly shutting off the supply of the conditioning factor at the ups. The method of maintaining a substantially per limit and maintainingit shut ofi while the condition of the medium remains above said upper limit, measuring during said shut off period the excess amount of said condition within the medium due to the previous admission of said conditioning factor. by timing the interval required for the condition toagain descend to the upper limit of the control zone and providing for the subsequent readmission of said conditioningfactor'in an amount reduced in ratio to said time interval, again admitting the condi-v tioning factor in such reduced amount as soon as the condition within the medium falls to the upper limit of the control zone by reason of the dissipation of the previous excess of the conditioning factor, increasing the rate of admission of the conditioning factor while the conditiono'f I the medium. remains below the lower limit of the control zone, and continuing said operations by stages which cause the conditioning of themedium to progressively approach the desired level by diminishing fluctuations until a stable condition within the control zone is attained. I

first supplying a condition factor to said medium at a predetermined and substantially even rate within the limits of a restricted control zone, promptly shutting on the supply of said condistable condition in a medium, which comprises tioning factor to said medium when the upper limit of said zone is reached, maintaining said supply shut off during the time the condition in said medium exceeds said upper limit, diminishing the succeeding supply rate according to the length of time the supply is shut off and again supplying the conditioning factor to said medium in such reduced amount when the. condition in said mediumfalls to said upper limit, increasing the rate' of supply of the conditioning factor while the condition of said medium remains below the lower limit of the control zone, and alternately continuing the adjusting operations for said supply until a substantially stable condition y within the control zoneisattained. I

. CARY H. STEVENSON. 

